Add isolate for content_browsertests with --site-per-process.

content/content_site_isolation_browsertests.isolate

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'includes': [
-    '../base/base.isolate',
+    'content_browsertests.isolate',
   ],
   'conditions': [
-    ['OS=="win" or OS=="mac" or OS=="linux"', {
+    ['OS=="linux"', {
       'variables': {
         'command': [
           '../testing/test_env.py',
-          '<(PRODUCT_DIR)/google_apis_unittests<(EXECUTABLE_SUFFIX)',
-          '--brave-new-test-launcher',
+          '<(PRODUCT_DIR)/content_browsertests<(EXECUTABLE_SUFFIX)',
           '--test-launcher-bot-mode',
-        ],
-        'files': [
-          '../testing/test_env.py',
-          'test/',
+                                        '--site-per-process',
+                                        '--test-launcher-filter-file=../testing/buildbot/filters/site-per-process.content_browsertests.filter',
         ],
       },
     }],
   ],
 }